Adequacy of power wheelchair control interfaces for persons with severe disabilities: A clinical survey

Linda Fehr, MS; W. Edwin Langbein, PhD; Steven B. Skaar, PhD

Hines VA Hospital, Rehabilitation Research and
Development Program, Research Service, Hines, IL 60141;
University of Notre Dame, Department of Aerospace and
Mechanical Engineering, Notre Dame, IN 46556

Abstract — The extreme difficulty with which
persons with severe disabilities have been taught to
maneuver a power wheelchair has been described in case
studies, and anecdotal evidence suggests the existence of a
patient population for whom mobility is severely limited if
not impossible given currently available power wheelchair
control interfaces. Since our review of the literature
provided little evidence either in support or refutation of
the adequacy of existing power wheelchair control
interfaces, we surveyed 200 practicing clinicians, asking
them to provide information about their patients and to give
their impressions of the potential usefulness of a new power
wheelchair navigation technology. Significant survey results
were:

Clinicians indicated that 9 to 10 percent of patients
who receive power wheelchair training find it extremely
difficult or impossible to use the wheelchair for activities
of daily living.

When asked specifically about steering and maneuvering
tasks, the percentage of patients reported to find these
difficult or impossible jumped to 40%.

Eighty-five percent of responding clinicians reported
seeing some number of patients each year who cannot use a
power wheelchair because they lack the requisite motor
skills, strength, or visual acuity. Of these clinicians, 32%
(27% of all respondents) reported seeing at least as many
patients who cannot use a power wheelchair as who can.

Nearly half of patients unable to control a power
wheelchair by conventional methods would benefit from an
automated navigation system, according to the clinicians who
treat them.

We believe these results indicate a need, not for more
innovation in steering interfaces, but for entirely new
technologies for supervised autonomous
navigation.

This material is based upon work supported by Hines VA Hospital, Rehabilitation Research and Development Center.
Address all correspondence and requests for reprints to: Linda Fehr, Hines VA Hospital, Rehabilitation Research and Development Program, Research Service, Hines, IL; email: linda.fehr@med.va.gov.

INTRODUCTION

With the advent of microprocessors,
significant innovation has occurred in power wheelchair
control interfaces. In addition to the more common
interfaces such as sip-and-puff and chin and head controls,
power wheelchair users have available to them such complex
control schemes as tongue touch pads and eye gaze systems.
Nevertheless, we suspect that, in spite of today's
sophisticated control interfaces, persons with severe and/or
multiple disabilities may yet find it prohibitively
difficult to steer a power wheelchair in typical
residential, institutional, or office settings in which
maneuvering space is limited, the approach to furniture and
objects is tightly constrained, and the necessity to
negotiate doorways requires precise control. In fact, case
studies have been reported, both in the literature and
anecdotally, of individuals with high-level spinal cord
injury (SCI), multiple sclerosis (MS), or brain injury (BI)
who have spent months, even years, learning to steer a power
wheelchair--in some cases, with only marginal results (1,2).
Further, an extensive review of the literature has produced
little insight into the number and characteristics of users
of power wheelchair control interfaces or the adequacy of
these control technologies.

An alternative strategy to seeking greater
innovation in the rider-wheelchair control interface is to
employ a combination of microprocessors/computers and
sensors that assist or completely assume control of power
wheelchair navigation at the discretion of the rider. From
the past 10 years of published literature, one finds at
least a dozen independent, research initiatives devoted to
the development of such navigation aids (3-14). The authors
are involved in the development of a Computer-Controlled
Power Wheelchair Navigation System (CPWNS), which relies on
video detection of environmental cues in combination with
wheel rotation information. This system promises to provide
the basis for safe, versatile, and robust autonomous
wheelchair control for persons with severe disabilities
(13). To better document the existence and nature of the
target patient population for this emerging technology, we
sent a short questionnaire and brief, informative videotape
describing the CPWNS to 200 clinicians, asking them to
provide information about their patients and to give their
impressions of the potential usefulness of this new
technology.

METHODS

We surveyed 200 practicing clinicians in a
variety of clinics, residential treatment facilities, and
rehabilitation hospitals. Efforts were made to survey a
variety of geographically dispersed facilities providing
inpatient, outpatient, and residential care for a wide range
of mobility-limiting conditions among persons of all ages.
Surveys were sent to the Spinal Cord Injury Centers, Blind
Centers, and Geriatric Rehabilitation and Extended Care
Centers (GRECCs) within Veteran's Health Services of the
Department of Veteran's Affairs. Survey recipients were also
selected from organizations listed by the National Multiple
Sclerosis Society, the Muscular Dystrophy Association, the
Amyotrophic Lateral Sclerosis Association, and the National
Directory of Head Injury Rehabilitation Services (15).
Additional surveys were sent to selected institutions listed
with the Commission on Accreditation of Rehabilitation
Facilities (CARF), based on information found in the
Directory of Medical Rehabilitation Programs (16), the
Medical and Health Information Directory (17), the Directory
of Nursing Homes (18), the Hospital Blue Book (19), and the
Healthcare Blue Book (20).

The questionnaire is presented in Appendix A. Each of the 200
recipients was sent a packet containing the questionnaire, a
postage-paid return envelope for the survey, and a 3-minute
videotape describing a computerized system for power
wheelchair navigation intended for persons with severe
disabilities. Packets were addressed personally to the
director of each facility or to the director of
rehabilitation services if the name of the incumbent was
available. A cover letter requested that the clinician view
the videotape and complete and return the questionnaire. The
letter asked that the clinician forward the packet to the
person most involved with wheelchair seating/training if, in
fact, the recipient was not that person. The recipient was
also encouraged to duplicate the survey if his/her
colleagues were willing to provide additional responses or
to return the survey marked "N/A" if none of the
questions applied to any segment of the institution's
patient population. A telephone number was provided to
enable recipients to obtain additional information or
additional packets, and recipients were given the option to
return the survey by fax. Each survey packet was numbered,
and recipients who did not respond within 60 days were sent
follow-up requests (letter only).

RESULTS

Survey Respondents
Sixty-five surveys (33 percent) were returned by
recipients. Of these, ten were blank or marked
"N/A". The remaining 55 surveys contained
information on patients with mobility impairments and are
summarized in this report.
Table 1 provides a profile of the types of facilities
surveyed. Comprehensive rehabilitation hospitals provide
care for a wide range of conditions including spinal cord
injury, brain injury, stroke, fractures, pulmonary disease,
neurological disorders, and musculoskeletal
diseases/injuries. Institutions specializing specifically in
brain injury, spinal cord injury, and/or stroke are listed
separately. Seven of the surveyed institutions were reported
as exclusively pediatric facilities, though, potentially
many others serve large numbers of children. As indicated,
survey respondents were representative of the surveyed
population as a whole with respect to type of institution.
Response rates for VA spinal cord injury centers and
facilities for the blind were slightly higher, while
responses from institutions providing comprehensive
rehabilitation were proportionately fewer.

Survey respondents appeared to be unbiased
with respect to both size and geographic distribution (see
Figure 1). Completed surveys were received from 29
states, the District of Columbia, and Puerto Rico.
Directories used to select survey recipients reported
institution size ("number of beds" or "number
of beds devoted to rehabilitation") for approximately
60% of the facilities surveyed.

Figure 1.
Geographic and size distributions of survey population and respondents.

An indication of size of the relevant patient
population in each responding institution was provided by
the questionnaire itself. Survey questions I.1 and I.2
sought to define, for each facility, the number of patients
who are power wheelchair users. These census figures were
used in subsequent analyses to weight responses to other
questions. For example, if one facility trains 100 patients
per year to use a power wheelchair and reports that 2
percent of these patients have difficulty using the chair,
while a second institution trains 10 patients, 20 percent of
whom have difficulty, the simple average of patients who
experience difficulty is 11 percent(2 percent+20 percent)/2)
but the weighted average is 3.6 percent((2
percent×100+20 percent×10)/110).

Nature and Adequacy of Power Wheelchair Control
Interfaces
The principal objective of our clinical survey
was to gain insight into the types of control interfaces
employed by power wheelchair users and the adequacy of these
controls. According to the clinicians who responded to our
survey, more than 95 percent of power wheelchair users
maneuver their chairs with joystick, sip-and-puff, head, or
chin controls (Table 2). Only eight respondents
reported having patients who use any other type of control
interface. Potential explanations for this phenomenon
include: a) clinicians are unaware of more sophisticated
control interfaces and, therefore, do not prescribe them;
(b) more sophisticated interfaces are not accepted by users,
perhaps because they are ineffective and/or prohibitively
difficult to use; or, (c) more sophisticated interfaces are
unnecessary because joystick, head control, and sip-and-puff
interfaces are adequate.

Table 2.

Power wheelchair control interfaces used (survey question
I.1).

Percent of patients using

Simple
Average(n=46)

Weighted*
Average(n=30)

Joystick

81

81

Head or chin control

9

9

Sip and Puff

6

9

Other
(eye gaze; tongue pad; head,
hand, foot switch controls

4

1

Total

100

100

* weighted by total number of power wheelchair users reported in survey question I.1.

The survey responses summarized in Tables
3 and 4 suggest that the power wheelchair control
interfaces used may not, in fact, be adequate to provide
truly independent mobility for substantial numbers of
persons with disabilities. Respondents to our survey
reported on average that approximately 10 percent of the
patients they train to operate a power wheelchair cannot use
the chair upon completion of training for activities of
daily living (ADL) or can do so only with extreme
difficulty. Clinicians also indicated that even among their
patients who are regular power wheelchair users, 40 percent
of these persons have difficulty with steering tasks such as
maneuvering the chair throughout the confines of a typical
home or office environment, including passage of doorways
and entering and exiting elevators. Further, clinicians
reported that between five and nine percent of regular power
wheelchair users find such tasks impossible without
assistance.

Table 3.

Adequacy of existing control interfaces.

Measure

Simple
Average

Weighted
Average

Percentage of patients who, after
training, have extreme difficulty using a power wheelchair for ADL

6

6*

Percentage of patients who, after
training, find it impossible to use a power wheelchair for ADL

4

3*

Total Percentage

10

9

(survey question
I.3)

(n=42)

(n=38)

Percent of power wheelchair users
who have difficulty with steering tasks

32

35**

Percent of power wheelchair users
for whom steering tasks are impossible without assistance

9

5**

Total Percentage

41

40

(survey question
I.4)

(n=49)

(n=32)

* weighted by numbers trained, reported in survey question I.2;
** weighted by total number of power wheelchair users reported in survey question I.1.

Table 4.

Proportion of patients unable to use a power wheelchair
(survey question I.5)

Measure

Simple
Average

Weighted
Average

Percentage of patients evaluated
annually who are not candidates for a power wheelchair because they lack requisite motor
skills, strength, or visual acuity

18*
(n=15)

26**
(n=44)

Percentage of these patients who
could benefit from a computer-controlled navigation system

49
(n=49)

44***
(n=45)

* mean of all responses to the first part of question I.5 given as a percentage;
** all responses to question I.5 (percentage or absolute number) weighted by the estimated
number of patients seen annually (see text); *** weighted by responses to questions I.2
and/or I.5.

Independent Mobility Options for Persons with Severe
Disabilities
In addition to assessing the adequacy of
available control interfaces for regular power wheelchair
users, our survey results also document the existence of a
group of persons for whom no independent mobility options
exist at this time. Eighty-five percent of responding
clinicians reported seeing some number of patients each year
for whom use of a power wheelchair is not an option because
these patients lack the motor skills, strength, or visual
acuity needed to control the chair. Twenty-seven percent of
respondents reported evaluating at least as many patients
who cannot use a power wheelchair as who can (i.e., the
number reported for question I.5 was greater than or equal
to the response to question I.2). It was estimated from
survey responses that 18-26 percent of nonambulatory
patients who cannot use a manual wheelchair are also unable
to operate a power wheelchair (see Table 4).
Clinicians indicated that nearly half their patients who are
unable to operate a power wheelchair using conventional
methods would benefit from a computer-controlled power
wheelchair navigation system.

A secondary objective of our survey was to
evaluate the perceived usefulness of an emerging technology
whereby a computer controls the steering of a power
wheelchair on behalf of its rider. As indicated above,
clinicians reported that 44-49 percent of their patients who
are unable to operate a power wheelchair would benefit from
this technology. Persons with spinal cord injury and
disorders such as MS, amyotrophic lateral sclerosis (ALS),
and Parkinson's disease, alone or in combination with other
disabilities, were the patient populations most frequently
cited by clinicians as likely to benefit. Further, when
asked to consider the possibility of enabling persons with
cognitive disabilities to travel unassisted to specified
locations within an institution at pre-programmed times (a
potential future application of computer-controlled
navigation), 91 percent believed such capability would be
useful for at least a few patients, and 23 percent believed
it would be useful for many.

DISCUSSION

There appeared to be no major
misinterpretations of survey questions that warranted
excluding significant amounts of data from analysis;
however, many respondents elected to leave some questions
blank. (Only 17 questionnaires were returned 100 percent
complete.) Blank responses were not assumed to represent
zero unless circumstances indicated this was the
respondent's intent.

Missing responses were taken into
consideration in presenting aggregate results. Specifically,
since responding institutions varied greatly with respect to
size, it was desirable to weight responses accordingly.
This, however, resulted in discarding the information
provided by numerous clinicians who opted not to answer
census questions I.1 and/or I.2. To avoid this loss of data,
both simple averages and weighted averages were reported. In
all cases but one, simple and weighted averages differed by
no more than five percentage points.

The only disparity greater than five
percentage points between simple versus weighted averages
occurred with the first part of survey question I.5
(patients who are not candidates for a power wheelchair).
Fifteen clinicians responded to the question with a
percentage, and the remainder with an absolute count. Since
five of the respondents who gave a percentage provided no
census data (questions I.1 or I.2), the percentages could
not be interpreted and were included only in the simple
average shown in Table 4 (18 percent). The average of
26 percent in Table 4 was obtained by weighting all
other responses (both percentages and absolute numbers) by
the total number of patients evaluated annually, which was
taken to be the sum of all patients trained to use a power
wheelchair (question I.2) plus those who were not candidates
for a power wheelchair (question I.5). Alternatively, if one
omits from this computation all responses given as
percentages, the resulting weighted average jumps to 36
percent (n=34).

Regardless of careful construction of the
questionnaire, data problems such as the foregoing are
inherent in survey methodology. Every effort was made to
manage these inconsistencies in a manner that did not
compromise the validity of the study findings.

CONCLUSION

According to survey respondents, the vast
majority of patients who use a power wheelchair rely on
joystick, sip-and-puff, chin, or head control interfaces.
Very sophisticated control technologies such as eye gaze or
tongue pad interfaces are employed by fewer than 5 percent
of power wheelchair users (perhaps as few as 1 percent).
This would indicate that individuals with severe
disabilities which compromise respiratory drive and/or limit
the dexterity of the head and hands have few options for
steering a power wheelchair. This notion is further
reinforced by the fact that 85 percent of respondents
reported evaluating some number of patients annually for
whom a power wheelchair is not an option because they cannot
control it. Of these clinicians, 32 percent indicated that
they evaluate at least as many patients who cannot use a
power wheelchair as patients who can. These include persons
with high-level SCI, nervous system diseases, cognitive
impairment, and blindness, presumably in conjunction with
mobility impairment. One must conclude that, for these
persons, no independent mobility options exist at this
time. Further, our clinical survey provides evidence
that existing control technologies may not be entirely
adequate even for persons who use a power wheelchair on a
regular basis. On average, responding clinicians reported
that approximately 40 percent of their patients who use
power wheelchairs have difficulty with steering tasks and
that between five and nine percent find such tasks
impossible without assistance.

One potential solution to the shortcomings of
power wheelchair control technologies is to enable a
computerized navigation system to assume control of steering
tasks at the behest of the rider. A computer-controlled
power wheelchair navigation system, which functions in a
well-defined but minimally modified environment, has been
developed at the University of Notre Dame, Automation and
Robotics Laboratory. The navigation system has repeatedly
demonstrated its ability to guide a power wheelchair along
the precise trajectories typically required within a home,
office, or institution with reliability approaching 100
percent. In a joint development project between the
University and the Rehabilitation Research and Development
Service of the Department of Veterans Affairs, investigators
are downsizing the original system and incorporating a
number of safety and convenience features, producing a
device suitable for patient testing. Persons with
disabilities who have difficulty operating a power
wheelchair will be recruited to test the new guidance system
and provide feedback for subsequent stages of development.
Because the navigation system is implemented using
relatively low-cost components that may be readily
retrofitted to an existing power wheelchair, the long-term
goal of the project is to produce a commercially viable
product at a reasonable price. Such a system would provide
persons with severe mobility impairments a degree of
autonomy not otherwise attainable.